Semiconductor image sensors are used to sense radiation such as light. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupled device (CCD) sensors are widely used in various applications such as digital still camera or mobile phone camera applications. These devices utilize an array of pixels (which may include photodiodes and transistors) in a substrate to absorb (i.e., sense) radiation that is projected toward the substrate and convert the sensed radiation into electrical signals.
A back side illuminated (BSI) image sensor device is one type of image sensor device. These BSI image sensor devices are operable to detect light from the backside. Compared to front side illuminated (FSI) image sensor devices, BSI image sensor devices have improved performance, especially under low light conditions. However, traditional methods of fabricating BSI image sensor devices may still lead to certain shortcomings for BSI image sensor devices. For example, the fabrication of traditional BSI image sensors generally forms a color filter array on a flat surface above a light-blocking metal grid. However, the disposition of the color filter array above the metal grid leads to a longer optical path for the light before it can be detected by a desired pixel. The disposition of the color filter array above the metal grid also requires accurate alignment between the color filter array and the metal grid, as any misalignment may cause undesirable cross-talk between adjacent pixels.
Hence, while existing BSI image sensor devices have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.